U.S. Pat. No. 6,592,895 is directed at precursor polyhydric alcohol esters where acyl moieties originate from aliphatic homopolymer or copolymer polyesters which contain free hydroxyl at their terminal ends where some or each of the free hydroxyls are reacted to provide 2-carboxy-ethenyl groups. These are indicated as being useful for the formation of hydrogels for delivery of drugs or other biologically active agents, for example, from hydrogel coating on vascular stents.